This invention relates to a process for producing an enriched oxygen gas from a mixed gas containing oxygen and nitrogen as main gas components, particularly air, by pressure swing adsorption.
An oxygen-enriched gas obtained by pressure swing adsorption can be supplied easily and continuously on site and at low cost to industries requiring continuous supply of a large amount of an oxygen gas, particularly steel manufacture using an electric furnace, oxygen aeration for water treatment, pulp bleaching, etc. Thus, the oxygen-enriched gas is more and more widely utilized.
In the conventional process for producing an oxygen-enriched gas by pressure swing adsorption, a pressure equalization step is provided as a means of enhancing the oxygen recovery rate, wherein a lower pressure column which has completed desorption and a higher pressure column which has completed adsorption are connected to each other and to transfer the gas remaining in the higher pressure column therefrom to the lower pressure column until the pressures in the two columns are equalized, whereby a gas having a higher oxygen concentration than that of the feed gas is recovered (U.S. Pat. Nos. 3,738,087 and 3,923,477). However, since the gas recovery is conducted until the pressures of the two columns become completely equal to each other, the transferred gas inevitably contains a large amount of nitrogen gas. Although the oxygen recovery rate is improved, the oxygen concentration of the product oxygen-enriched gas is lowered. Thus, it has been so far desired to overcome the reduction of oxygen concentration of the product oxygen-enriched gas by pressure equalization.